Rapid prototyping involves the production of prototype articles and small quantities of functional parts, as well as structural ceramics and ceramic shell molds for metal casting, directly from computer-generated design data. There are a variety of methods to form a three-dimensional article including a selective laser-sintering process as described in U.S. Pat. No. 4,863,568, which is incorporated herein by reference.
Three-dimensional printing is a process invented by Sachs et al. at Massachusetts Institute of Technology in the early 1980's. In accordance with the process, an ink-jet printhead is used to deposit a liquid ink or binder onto a print plane composed of a powdered receiving medium. The combination of liquid binder and solid powder solidifies to form a finished article.
U.S. Pat. No. 5,204,055, incorporated herein by reference, describes an early three-dimensional printing technique that involves the use of an ink-jet printing head to deliver a liquid or colloidal binder material to layers of powdered material. The three-dimensional inkjet printing technique (hereafter “liquid-binder method”) involves applying a layer of a powdered material to a surface using a counter roller. After the powdered material is applied to the surface, the ink-jet printhead delivers a liquid binder to the layer of powder. The binder infiltrates into gaps in the powder material, hardening to bond the powder material into a solidified layer. The hardened binder also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the previous steps are repeated, building successive cross-sectional portions until the final article is formed. Optionally, the binder can be suspended in a carrier that evaporates, leaving the hardened binder behind. The powdered material can be ceramic, metal, plastic or a composite material, and can also include fiber. The liquid-binder material can be organic or inorganic. Typical organic binder materials used are polymeric resins, or ceramic precursors such as polycarbosilazane. Inorganic binders are used where the binder is incorporated into the final articles; silica is typically used in such an application.
In the technology of ink-jet printing, there are a number of different types of printheads distinguished by the mechanism by which ink is ejected onto the printing plane. The two broadest classes of printheads are called, “continuous-jet” and “drop-on-demand.” In a continuous-jet printhead, a liquid ink or binder is projected continuously through a nozzle. To print segmented lines, the jet is deflected alternatively onto the print plane or in to a collector that masks the printing plane. In a drop-on-demand printhead, ink or binder is ejected when it is needed by sending an impulse, most usually electrical, that causes an actuator in the printhead to eject a droplet of ink or binder onto the print plane.